The US president, George Bush, flew into Rome last night as the Italian prime minister, Silvio Berlusconi, expressed concern that anti-war marches today could end in violence.

Mr Berlusconi, in a broadcast carried live on Italian television, urged demonstrators to show restraint. He said he was "worried about the possible violence" and said that a police report assessing the situation "does not leave us calm".

Huge marches are planned in the capital in protest against the war in Iraq.

Mr Bush is in Rome to mark the 60th anniversary of the liberation of the city by the Allies today, and will continue to Normandy to mark the anniversary of the D-day landings on Sunday.

The authorities have given protesters permission to march through the centre of the city in an attempt to ease tension. The route will go nowhere near Mr Bush.

It is Mr Bush's first visit to Europe since London last November when there was also a mass anti-war demonstration. In an interview with Italian television ahead of his trip, Mr Bush insisted, as he had in London, that protest was a healthy sign of democracy.

But unprecedented security measures were being put into force yesterday in the Italian capital: 10,000 police will be deployed, airports will be closed this afternoon to clear airspace over the city, sewers have been searched and sealed and monuments will be manned by snipers.

Achille Serra, a senior security official, said yesterday that no terrorist threats have been received "but I have had indications that public order might be difficult".

Mr Serra said that many anti-globalisation groups were expected to travel to Rome, including anarchist groups blamed for some of the violence in Genoa in 2001 when the centre of city was trashed and a protester was killed in battles with police.

Mr Serra said policing Rome would be difficult: "When the scene is so mixed, and especially when demonstrations are planned in different locations in the city, it becomes difficult to predict."

Rainbow peace flags have reappeared in force in windows throughout Rome and posters crying, "Liberate Rome from Bush" and "Bush go home" are plastered on walls.

The US embassy warned Americans to avoid the crowds massed for the protests. "Not all demonstrations are expected to be peaceful. There is a potential for violence," it said in a statement.

Mr Berlusconi, the right-wing media magnate who has been one of Mr Bush's strongest supporters in Europe, along with Mr Blair, said: "I am concerned by the conviction among some youths that burning a flag, smashing a window or worse gives more force to their ideas. Exactly the opposite is true."

He urged the country to "show the world its hospitality, its maturity, its awareness of history" by welcoming Mr Bush. "Beyond any political judgment on the military intervention in Iraq, it is our duty to welcome him as the leader of a great nation that is our friend and ally," he said.